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Subject: Re: [RFC] Tracer Ring Buffer splice() vs page cache [was: Re: Perf
 and ftrace [was Re: PyTimechart]]
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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On Mon, 2010-05-17 at 18:42 -0400, Mathieu Desnoyers wrote:
> I'll continue to look into this. One of the things I noticed that that we could
> possibly use the "steal()" operation to steal the pages back from the page cache
> to repopulate the ring buffer rather than continuously allocating new pages. If
> steal() fails for some reasons, then we can fall back on page allocation. I'm
> not sure it is safe to assume anything about pages being in the page cache
> though. 

Also, suppose it was still in the page-cache and still dirty, a steal()
would then punch a hole in the file.

> Maybe the safest route is to just allocate new pages for now.

Yes, that seems to be the only sane approach.